Image pickup device, its control method, and camera

ABSTRACT

An image pickup device, wherein a part of the carriers overflowing from the photoelectric conversion unit for a period of photoelectrically generating and accumulating the carriers may be flowed into the floating diffusion region, and a pixel signal generating unit generating a pixel signal according to the carriers stored in the photoelectric conversion unit and the carriers having overflowed into the floating diffusion region, is provided. The expansion of a dynamic range and the improvement of an image quality can be provided by controlling a ratio of the carriers flowing into the floating diffusion region to the carriers overflowing from such a photoelectric conversion unit at high accuracy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup device, its controlmethod, and a camera.

2. Related Background Art

The specification of U.S. Pat. No. 6,307,195 discloses an image pickupdevice in which carriers having overflowed from a photodiode while photocarriers are being accumulated overflow into a floating diffusion (FD)region through a transfer gate (TG). In the image pickup device, a partof the carriers having flowed into the floating diffusion region isdiscarded for expanding the dynamic range of the device. Accordingly,the accumulation time of the floating diffusion region is set to beshorter than the accumulation time of the photodiode. In theconfiguration described above, it is stated that the dynamic range canbe expanded by shortening the accumulation time of the floatingdiffusion region. However, all of the pieces of information of carrierswhich have flowed from the photodiode into the floating diffusion regionfor a period from the start of the accumulation time of the photodiodeto the start of the accumulation time of the floating diffusion regionare lost. Consequently, an image different from the image which a personactually viewed is picked up.

Moreover, Japanese Patent Application Laid-Open No. 2004-335803discloses a MOS type image pickup device in which plural light receivingunits are arranged on the surface of a semiconductor substrate in theshape of an array and the signal of each light receiving unit is readfrom each light receiving unit. The image pickup device includes a firstsignal carrier detection unit which detects incident light to output asignal according to the quantity of the detected incident light.Moreover, the image pickup device includes a second signal carrierdetection unit which traps a part of excess carriers of the first signalcarrier detection unit when the detection signal of the first signalcarrier detection unit has saturated to output a signal according to thequantity of the trapped carriers.

As shown in Japanese Patent Application Laid-Open No. 2004-335803, thesecond signal carrier detection unit (38), which detects a part ofsaturated electrons generated in the first signal carrier detection unit(31) when the electrons have saturated, is independently formed.Moreover, the image pickup device has the structure of trapping a partof excess carriers to discard the residual carriers into a verticaloverflow drain.

However, in order to discard a part of generated carriers to thevertical overflow drain and to collect the remainder to the secondsignal carrier detection unit (38), a technique of manufacturing thebarrier unit (33) and the vertical overflow drain in a manner of havingpotential in very high accuracy is necessary. Because dispersion arisesin each sample and an inflow rate changes when the accuracy is notadequate, the structure has a drawback of lacking mass productivityremarkably.

Moreover, because the structure is one in which the discharging side ofcarriers is the vertical overflow drain and the trapping side ofcarriers is a lateral overflow drain, the carriers are required to goover a barrier between the different structures. Consequently, thestructure has a drawback such that the ratio of the carriers flowing outto the vertical overflow drain and the lateral overflow drain hastemperature dependence.

SUMMARY OF THE INVENTION

An image pickup device according to the present invention includes: aphotoelectric conversion unit generating carriers by photoelectricconversion to accumulate the carriers; a transfer transistor fortransferring the carriers of the photoelectric conversion unit; afloating diffusion region into which the carriers are transferred by thetransfer transistor; a transfer gate control unit controlling a gatevoltage of the transfer transistor so that a part of the carriersoverflowing from the photoelectric conversion unit for a period in whichthe photoelectric conversion unit is generating and accumulating thecarriers may flow into the floating diffusion region; and a pixel signalgenerating unit generating a pixel signal according to the carriersaccumulated in the photoelectric conversion unit and the part of thecarriers having overflowed into the floating diffusion region.

An image pickup device according to the present invention includes: aphotoelectric conversion unit generating carriers by photoelectricconversion to accumulate the carriers; a transfer transistor fortransferring the carriers of the photoelectric conversion unit; afloating diffusion region into which the carriers are transferred by thetransfer transistor; a transfer gate control unit controlling a gatevoltage of the transfer transistor to be any of a first gate voltage atwhich the transfer transistor is turned on, a second gate voltage atwhich the transfer transistor is turned off, and a third gate voltagebetween the first and the second gate voltages; and a pixel signalgenerating unit generating a pixel signal according to the carrierstransferred into the floating diffusion region in a period in which thegate voltage is controlled to be the first gate voltage and the thirdgate voltage.

An image pickup device according to the present invention includes: aphotoelectric conversion unit generating carriers by photoelectricconversion to accumulate the carriers; a transfer transistor fortransferring the carriers of the photoelectric conversion unit; afloating diffusion region into which the carriers are transferred by thetransfer transistor; a transfer gate control unit controlling a gatevoltage of the transfer transistor so that a part of the carriersoverflowing from the photoelectric conversion unit for a period in whichthe photoelectric conversion unit is generating and accumulating thecarriers may flow into the floating diffusion region; and a pixel signalgenerating unit generating a pixel signal according to the carriersaccumulated in the photoelectric conversion unit and the part of thecarriers having overflowed into the floating diffusion region.

Moreover, a control method of an image pickup device according to thepresent invention is a control method of an image pickup device providedwith a photoelectric conversion unit generating carriers byphotoelectric conversion to accumulate the carriers, a transfertransistor for transferring a signal of the photoelectric conversionunit, and a floating diffusion region into which the carriers aretransferred by the transfer transistor, the method comprising: atransfer gate control step of controlling a gate voltage of the transfertransistor so that a part of the carriers overflowing from thephotoelectric conversion unit for a period in which the photoelectricconversion unit is generating and accumulating the carriers may flowinto the floating diffusion region; and a pixel signal generating stepof generating a pixel signal according to the carriers accumulated inthe photoelectric conversion unit and the part of the carriers havingoverflowed into the floating diffusion region.

Moreover, a camera according to the present invention includes: theimage pickup device described above; a lens for focusing an opticalimage on the image pickup device; and a diaphragm for changing a lightquantity passing through the lens.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a layout chart showing a configuration example of pixel unitsof an image pickup device according to a first embodiment of the presentinvention;

FIG. 2 is a potential diagram of the cross sections taken along an O-Aline, an O-B line and an O-C line in FIG. 1 during a carrier storingperiod;

FIG. 3 is a layout chart showing an example of the whole configurationof the image pickup device according to the present embodiment;

FIG. 4 is an equivalent circuit diagram of the image pickup device ofFIG. 3;

FIG. 5 is a timing chart showing an operation example of the circuit ofFIG. 4;

FIG. 6 a block diagram showing a configuration example of a still videocamera according to a second embodiment of the present invention; and

FIG. 7 is a block diagram showing a configuration example of a videocamera according to a third embodiment of the present invention.

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

FIG. 1 is a layout chart showing a configuration example of pixel unitsof an image pickup device according to a first embodiment of the presentinvention, and FIG. 2 is a potential diagram of the cross sections takenalong an O-A line, an O-B line and an O-C line in FIG. 1 during acarrier storing period. In the following, an n-channel MOS field effecttransistor is simply referred to as a MOS transistor. In the imagepickup device, plural pixels are two-dimensionally arranged. FIG. 1 is aplan view showing arranged four pixels as an example. One pixel includesa transfer MOS transistor Tx-MOS and a reset MOS transistor RES-MOS.Furthermore, the pixel includes a source follower MOS transistor SF-MOSand a selection MOS transistor SEL-MOS. A photo-diode PD and a floatingdiffusion region FD correspond to a source and a drain of the transferMOS transistor Tx-MOS, respectively. A drain B of the transistor RES-MOSis connected to a fixed power source voltage VDD.

The photodiode PD, which functions as a photoelectric conversion unit,generates carriers by photoelectric conversion, and stores the generatedcarriers. A gate of the transfer MOS transistor Tx-MOS is a gate fortransferring the carriers generated by the photodiode PD to the floatingdiffusion region FD, which is a diffusion region. By closing thetransfer gate (by turning off the transistor Tx-MOS), the photodiode PDcan generate and stored carriers by photoelectric conversion. When theaccumulation time ends, the carriers stored in the photodiode PD can betransferred (read) to the floating diffusion region FD by opening thetransfer gate (by turning on the transistor Tx-MOS).

In FIG. 2, a region a denoted by the O-A line indicates the potentialbetween the photodiode PD and the floating diffusion region FD (i.e. thepotential under the gate of the transistor Tx-MOS). A point O denotesthe potential of the photodiode PD, and a point A denotes the potentialof the floating diffusion region FD of the same pixel as that of thephotodiode PD.

Similarly, in FIG. 2, a region b denoted by the O-B line indicates thepotential between the photodiode PD and the drain B of the transistorRES-MOS. A point B indicates the drain B of the transistor RES-MOS.

A region c denotes by the O-C line of FIG. 2 indicates the potentialbetween the photodiode PD of a certain pixel and another pixel adjoiningto the photodiode PD. A point C denotes the potential of the floatingdiffusion region FD of the adjoining pixel.

Here, potential is one of the barriers. One of the methods ofcontrolling a barrier is controlling potential. The potential iscontrollable by an impurity density or a gate voltage.

The height of the potential enclosing the photodiode PD is the sameheight as that of the region c except for the regions a and b. Thepotential of the region b is made lower than the potential of region c.The photodiode PD includes an n-type region storing electrons ascarriers. The regions b and c are p+ type regions. As described above,the potential of these regions can be controlled by adjusting theimpurity density. On the other hand, the potential of the region a canbe changed by controlling the potential of the transfer gate of thetransistor Tx-MOS. For a period in which the photodiode PD is generatingand storing the carriers, the potential of the region a is made to havethe same height as that of the potential of the region b. The potentialof the regions a and b are controlled to be the lowest among thebarriers enclosing the photodiode PD. Moreover, the potential of each ofthe regions a and b may be controlled independently.

The quantity of the carriers which the photodiode PD can store isdetermined. Consequently, when strong light is radiated to thephotodiode PD, carriers overflow from the photodiode PD. The carriershaving overflowed from the photodiode PD flow, being divided into thefloating diffusion region FD and the drain B of the transistor RES-MOS.That is, a part of the carriers flows into the floating diffusion regionFD, and the other part of the carriers is ejected to the drain B of thetransistor RES-MOS.

In the present embodiment, a part of the overflowed carriers can begathered into the floating diffusion region FD at a certain fixed ratio.The carriers having overflowed from the photodiode PD flows into thefloating diffusion region FD at the point A through the region a havingthe lowest potential. By controlling the potential in the region a tobecome the same as the potential in the region b, the carriers havingoverflowed from the photodiode D can be distributed to the regions a andb at the same ratio. Moreover, the region b is preferably the fixedpower source voltage VDD. The reason is that the carriers having flowedinto the drain B can be processed promptly.

The region c is the floating diffusion region FD of the adjoining pixel.The region c forming the barrier of this part requires higher potentialcompared with the potential of the region b. The reason is that theleakage of the carriers into the adjoining pixel region can besuppressed by such a measure.

The ratio of the distribution the carriers flowing into the regions of aand b may be controlled by the ratio of the gate width W of transfer MOStransistor Tx-MOS and the width Wb of the region b. Moreover, bycontrolling the gate voltage of the transfer MOS transistor Tx-MOS so asto be a desired ratio of the distribution of the carriers, thedistribution of the carriers can be performed by a stable ratio. And itbecomes possible to attain the expansion of the dynamic range. Forexample, it is also possible to make 10% of the carriers havingoverflowed from the photodiode PD flow into the carriers flow into thedrain B.

That is, it is possible to control the ratio of the carriers to bediscarded and signal carriers with higher accuracy compared with that ofthe related art disclosed in Japanese Patent Application Laid-Open No.2004-335803. Furthermore, in the present embodiment, because the mutualstructures of regions a and b are the same lateral direction overflowdrains, temperature dependence is small, and even if a change of theratio arises, the ratio can be maintained at a fixed value bycontrolling the potential.

FIG. 3 is a layout chart showing an example of the whole configurationof the image pickup device according to the present embodiment, and FIG.4 is an equivalent circuit diagram showing a certain pixel of the imagepickup device of FIG. 3. In FIG. 4, the floating diffusion region FD isconnected with the drain of the transfer MOS transistor Tx-MOS, thesource of the reset MOS transistor RES-MOS, and the gate of the sourcefollower MOS transistor.

FIG. 5 is a timing chart showing an operation example of the circuit ofFIG. 4. Potential φres indicates the gate voltage of the reset MOStransistor RES-MOS; potential φtx indicates the gate voltage of thetransfer MOS transistor Tx-MOS; potential φsel indicates the gatevoltage of the selection MOS transistor SEL-MOS; potential φCtsFDindicates the gate voltage of a MOS transistor 411; potential φCtnindicates the gate voltage of a MOS transistor 413; and potential φCtsPDindicates the gate voltage of a MOS transistor 412.

Before timing T1, the potential φres is positive potential, and thepotential φtx, φsel, φCtsFD, φCtn and φCtsPD are 0 V. The reset MOStransistor RES-MOS is turned on, and the power source voltage VDD issupplied to the floating diffusion region FD.

Next, a positive pulse is applied as the potential φtx. The transistorTx-MOS is turned on, and the power source voltage VDD is applied to thefloating diffusion region FD and the photodiode PD. Then, the floatingdiffusion region FD and the photodiode PD are reset. After the reset,the potential φres is lowered to 0 V, and the reset MOS transistorRES-MOS is turned off. Then, the potential φtx is set to, for example,−1.3 V, and the potential of the region a is made to be higher than thepotential of the region b. Thus, the photodiode PD and the floatingdiffusion region FD are made to be in a floating state. However, anexternal mechanical shutter is not opened yet at this time, and theaccumulation of photo carriers is not started in the photodiode PD.

Next, at timing T2, a mechanical shutter 53 (FIG. 6) opens, and light isradiated to the photodiode PD. Then, the photodiode PD starts generatingand storing photo carriers. At this time, the potential φtx is raisedto, for example, 0.7 V which is a value between a positive pulse appliedat a timing T1 and a voltage −1.3 V applied thereafter. And thepotential of the region a is made to be the same height as that of thepotential of the region b. Moreover, the potential φtx may be controlledto set the potential of the region a independently of the potential ofthe region b in case of some values of the ratio of the carriers havingoverflowed into the floating diffusion region FD.

Next, the dotted line of the potential of the floating diffusion regionFD at timing T3 indicates the potential when strong light is radiated.At the timing T3, the photodiode PD saturates, and a part of thenegative carriers of the photodiode PD flows from the photodiode PD intothe floating diffusion region FD. Thereby, the potential of the floatingdiffusion region FD lowers. A part of the carriers having overflowedfrom the photodiode PD flows into the floating diffusion region FD at acertain ratio, and the remainder is ejected by the power source voltageVDD of the drain B. Incidentally, the solid line of the potential of thefloating diffusion region FD indicates a case where weak light isradiated and the carriers do not overflow from the photodiode PD intothe floating diffusion region FD.

Next, at timing T4, the shutter 53 closes, and the photodiode PD isshielded from the light. Then, the generation of the photo carriers ofthe photodiode PD ends. And the potential φtx is lowered to, forexample, −1.3 V, and the potential of the region a is made to be higherthan the potential of region b. Thus, the photodiode PD and the floatingdiffusion region FD are made to be in a floating state. Because theinflow of the photo carriers of the photodiode PD into the floatingdiffusion region FD stops at this time point, the potential of thefloating diffusion region FD is maintained in this state.

Next, the potential φsel is made from 0 V to positive potential attiming T5. The selection MOS transistor SEL-MOS is turned on, and makesa signal output line 401 be in an active state. The source follower MOStransistor SF-MOS constitutes a source follower amplifier, and outputs avoltage to the signal output line 401 according to the potential of thefloating diffusion region FD.

Next, at timing T6, a positive pulse is applied as the potential φCtsFD.A transistor 411 is turned on, and the output according to the potentialof the floating diffusion region FD is stored in capacity CtsFD. Becausecarriers do not overflow into the floating diffusion region FD in apixel in which the photodiode PD is not saturated, the output accordingto the power source voltage VDD, which resets the floating diffusionregion FD, is stored in the capacity CtsFD. Moreover, when strong lighthas been radiated to the photodiode PD and the photodiode PD hassaturated, an output voltage lower than the power source voltage VDD,which resets the floating diffusion region FD, is stored in capacityCtsFD.

Next, at timing T7, a positive pulse is applied as the potential φres.The reset MOS transistor RES-MOS is turned on, and the floatingdiffusion region FD is again reset by the power source voltage VDD.

Next, at timing T8, a positive pulse is applied as the potential φCtn.The MOS transistor 413 is turned on, and an offset noise voltage in thestate in which the floating diffusion region FD is reset is stored incapacity Ctn.

Next, at timing T9, a positive pulse is applied as potential φtx. Thetransfer MOS transistor Tx-MOS is turned on, and the carriers stored inthe photodiode PD is read into the floating diffusion region FD.

Next, at timing T10, a positive pulse is applied as the potentialφCtsPD. The MOS transistor 412 is turned on, and the voltage of thesignal output line 401 according to the carriers having been read fromthe photodiode PD into the floating diffusion region FD is stored incapacity CtsPD.

Next, at timing T11, the potential φsel is made to be 0 V. The selectionMOS transistor SEL-MOS is turned off, and the signal output line 401becomes in an inactive state.

Next, at timing T12, the potential φres is changed to be positivepotential. The reset MOS transistor RES-MOS is turned on, and thepotential of the floating diffusion region FD is fixed to the powersource voltage VDD.

By the processing described above, the voltage corresponding to offsetnoises is stored in the capacity Ctn; the voltage corresponding to thecarriers having overflowed from photodiode PD into the floatingdiffusion region FD is stored in the capacity CtsFD; and the voltagecorresponding to the accumulated carriers of the photodiode PD is storedin the capacity CtsPD.

A differential amplifier 421 outputs a voltage generated by subtractingthe noise voltage of the capacity Ctn from the signal voltage of thecapacity CtsFD. A differential amplifier 422 outputs a voltage generatedby subtracting the noise voltage of the capacity Ctn from the signalvoltage of the capacity CtsPD. An amplifier 423 amplifies the outputsignal of the differential amplifier 421. An amplifier 424 amplifies theoutput signal of the differential amplifier 422.

The amplification degrees (gains) of the amplifiers 423 and 424 aredetermined by the ratio of the quantity of the carriers having flowedinto the floating diffusion region FD and the quantity of the carriershaving flowed into the drain B among the carriers having overflowed fromthe photodiode PD. For example, a case is described in which 10% of thecarriers having overflowed from the photodiode PD flows into thefloating diffusion region FD and 90% of the carriers flows into thedrain B. In that case, the amplifier 423 amplifies the input signal tentimes to output the amplified input signal, and the amplifier 424amplifies an input signal one time to output the amplified input signal.That is, that case means that 10 times of the quantity of the carriershaving overflowed into the floating diffusion region FD is the quantityof the carriers having overflowed from the photodiode PD.

An adder 425 adds the output signals of the amplifiers 423 and 424 tooutput the added signal as a pixel signal. Accordingly, the adder 425operates as a pixel signal generating unit. Because the pixel signal isgenerated based on the carriers stored in the photodiode PD and thecarriers having overflowed into the floating diffusion region FD, thedynamic range of the pixel signal can be more expanded compared with thecase where only the carriers stored in the photodiode PD are used. And,the pixel signal or image signal may be generated based on only thecarriers having overflowed into the floating diffusion region FD.

An amplifier 426 amplifies and outputs the output signal of the adder425 according to ISO speed. When the ISO speed is fixed at small number,the amplification degree is small, and when the ISO speed is fixed atlarge number, the amplification degree is large.

Moreover, in FIG. 2, when the ISO speed is fixed at 100, the potentialof the region a may be controlled to be the same height as that of thepotential of the region b, and when the ISO speed is fixed at 200 ormore, the height of the potential of the region a may be controlled tobecome higher than that of the potential of the region b. Moreover, inFIG. 5, when the ISO speed is fixed at 100, the potential φtx iscontrolled so that the height in the period from the timing T2 to T4 maybecome higher than the heights before the timing T2 and after the timingT4. On the other hand, when the ISO speed is fixed at 200 or more, thepotential φtx is controlled so that the height of the period from thetiming T2 to T4 may become the same as those before the timing T2 andafter the timing T4.

In other words, when the ISO speed is fixed at 100, the potential of theregion a is controlled so that the height in the period from the timingT2 to T4 may become lower than the heights before the timing T2 andafter the timing T4. On the other hand, when the ISO speed is fixed at200 or more, the potential of the region a is controlled so that theheight in the period from the timing T2 to T4 may become the same asthose before the timing T2 and after the timing T4.

As described above, the potential φtx of the transfer gate in the periodfrom the timing T2 to T4, in which the photodiode PD is generating andstoring carriers, is controlled according to the amplification degree ofthe pixel signal corresponding to the ISO speed.

Second Embodiment

FIG. 6 is a block diagram showing a configuration example of a stillvideo camera according to a second embodiment of the present invention.Based on FIG. 6, an example at the time of applying the image pickupdevice of the first embodiment to the still video camera is described infull detail. An image pickup device 54 and a circuit 55 processing animage pickup signal correspond to the above image pickup device.

In FIG. 6, a reference numeral 51 denotes a barrier used as a protectorand a main switch of a lens commonly. A reference numeral 52 denotes alens focusing an optical image of a subject on the image pickup device54. A reference numeral 53 denotes a diaphragm and shutter for changingthe quantity of the light having passed through the lens 52. And thereference numeral 54 denotes the image pickup device for capturing thesubject focused by the lens 52 as an image signal. The reference numeral55 denotes the circuit for processing an image pickup signal whichperforms the analog signal processing of the image pickup signal (imagesignal) output from the image pickup device 54. Furthermore, a referencenumeral 56 denotes an A/D converter performing the analog-to-digitalconversion of the image signal output from the circuit 55 processing theimage pickup signal. Moreover, a reference numeral 57 denotes a signalprocessing unit performing various corrections and data compression ofimage data output from the A/D converter 56. A reference numeral 58denotes a timing generator outputting various timing signals to theimage pickup device 54, the circuit 55 processing the image pickupsignal, the A/D converter 56 and the signal processing unit 57. Areference numeral 59 denotes a unit controlling the whole and arithmeticoperations which controls various arithmetic operations and the wholestill video camera. A reference numeral 60 denotes a memory unit forstoring image data temporarily. A reference numeral 61 denotes aninterface unit for performing the recording or the reading of arecording medium 62. The reference numeral 62 denotes the recordingmedium capable of attaching and detaching semiconductor memories or thelike for performing the recording or the reading of image data. Areference numeral 63 denotes an interface unit for communicating with anexternal computer and the like.

Here, the image pickup device, and the timing generator 58 and the likemay be formed in the same chip.

Next, the operation of the still video camera at the time ofphotographing in the configuration mentioned above is described. Whenthe barrier 51 is opened, a main power source is turned on, and then thepower source of a control system is turned on. Furthermore, the powersource of image pickup system circuits such as the A/D converter 56 isturned on. And in order to control light exposure, the unit 59controlling the whole and arithmetic operations releases the diaphragm(shutter) 53. Then, after a signal having been output from the imagepickup device 54 is converted by the A/D converter 56 through thecircuit 55 processing the image pickup signal, the signal is input intothe signal processing unit 57. An arithmetic operation of exposure isperformed in the unit 59 controlling the whole and arithmetic operationsbased on the data. The brightness is judged based on the result of thephotometry, and the unit 59 controlling the whole and arithmeticoperations controls the diaphragm 53 according to the result of thejudgment.

Next, high frequency components are taken out based on the signal outputfrom the image pickup device 54, and an arithmetic operation of thedistance to a subject is performed in the unit 59 controlling the wholeand arithmetic operations. After that, the lens is driven to judgewhether the lens is in-focus or not. When it is judged that the lens isnot in-focus, the lens is again driven to perform the judgment. Andafter the confirmation of the in-focus state, main exposure is started.When the exposure ends, the image signal output from the solid stateimage pickup device 54 passes the circuit 55 processing the image pickupsignal, and is subjected to the A/D conversion of the A/D converter 56.Then, the converted signal passes the signal processing unit 57, and iswritten in the memory unit 60 by the unit 59 controlling the whole andarithmetic operations. After that, the data stored in the memory part 60passes the I/F unit 61 controlling the recording medium to be recordedon the detachably attachable recording medium 62 such as a semiconductormemory or the like by the control of the unit 59 controlling the wholeand arithmetic operations. Moreover, the data may be directly input intoa computer or the like through the external I/F unit 63, and an imagemay be processed.

The timing generator 58 controls signals of FIG. 5 such as the potentialφres, φtx, φsel φCtsFD, φCtn, φCtsPD and the like. A thermometer 64detects a temperature, and outputs a voltage according to the detectedtemperature to the unit 59 controlling the whole and arithmeticoperations. The unit 59 controlling the whole and arithmetic operationsand the timing generator 58 control the potential φtx of the transfergate according to the temperature in the period from the timing T2 toT4, in which the photodiode PD is generating and storing carriers. Thatis, the unit 59 controlling the whole and arithmetic operations and thetiming generator 58 control in the period from the timing T2 to T4 sothat the potential of the region a may have the same height as theheight of the potential of the region b. But, because the height ofpotential changes dependently on temperature, the unit 59 controllingthe whole and arithmetic operations and the timing generator 58 cancontrol the height of the potential of the region a to be the sameheight as that of the potential of the region b by controlling thepotential φtx of the transfer gate according to the temperature.

Third Embodiment

FIG. 7 is a block diagram showing a configuration example of a videocamera according to a third embodiment of the present invention. Basedon FIG. 7, an embodiment in the case where the image pickup device ofthe first embodiment is applied to a video camera is described in fulldetail.

A reference numeral 1 denotes a photographing lens equipped with a focuslens 1A for performing a focus adjustment, a zoom lens 1B performing azoom operation, and a lens 1C for image formation. A reference numeral 2denotes a diaphragm and shutter. A reference numeral 3 denotes an imagepickup device performing the photoelectric conversion of a subject imageformed as an image on the image pickup surface thereof to convert thesubject image into an electric image pickup signal. A reference numeral4 denotes a sample hold circuit (S/H circuit) which performs the samplehold of the image pickup signal output from the image pickup device 3and further amplifies the level. The S/H circuit 4 outputs an imagesignal.

A reference numeral 5 denotes a process circuit which performspredetermined processing such as a gamma correction, a color separation,blanking processing and the like to the image signal output from thesample hold circuit 4. The process circuit 5 outputs a luminance signalY and a chroma (chrominance) signal C. The chroma signal C output fromthe process circuit 5 receives the corrections of white balance andcolor balance by a color signal correcting circuit 21, and the correctedsignal is output as color difference signals R-Y and B-Y.

Moreover, the luminance signal Y output from the process circuit 5 andthe color difference signals R-Y and B-Y output from the color signalcorrecting circuit 21 are modulated by an encoder circuit (ENC circuit)24, and are output as a standard television signal. And the standardtelevision signal is output a not shown video recorder, or an electronicview finder such as a monitor electronic view finder (EVF).

Subsequently, a reference numeral 6 denotes an iris control circuit,which controls an iris drive circuit 7 based on the image signalsupplied from the sample hold circuit 4 to automatically control an igmeter 8 in order to control the opening quantity of the diaphragm 2 sothat the level of the image signal may take a fixed value of apredetermined level.

Reference numerals 13 and 14 denote band path filters (BPF) havingdifferent band limiting extracting high frequency components requiredfor in-focus detection from the image signals output from the samplehold circuit 4. The signals output from the first band path filter 13(BPF 1) and the second band path filter 14 (BPF 2) are gated by each ofa gate circuit 15 and a focus gate frame signal, and the peak values ofthe gated signals are detected and held by a peak detecting circuit 16to be input into a logic control circuit 17. Each of the peak values iscalled as a focus voltage, and a focus is adjusted by means of the focusvoltage.

Moreover, a reference numeral 18 denotes a focus encoder detecting amovement position of the focus lens 1A. A reference numeral 19 denotes azoom encoder detecting a focus distance of the zoom lens 1B. A referencenumeral 20 denotes an iris encoder detecting the opening quantity of thediaphragm 2. The detection values of these encoders are supplied to thelogic control circuit 17 performing system control.

The logic control circuit 17 performs in-focus detection to a subject toperform focus adjustment based on the image signal corresponding to aset in-focus detection region. Specifically, the logic control circuit17 first captures the peak value information of the high frequencycomponents supplied from each of the band path filters 13 and 14. Andfor driving the focus lens 1A to a position where the peak value of thehigh frequency components becomes the maximum, the logic control circuit17 supplies control signals of the focus motor 10 such as the rotationdirection, the rotation speed and the rotation/stop to the focus drivingcircuit 9 to control the focus drive circuit 9.

A zoom drive circuit 11 rotates a zoom motor 12 when zoom is instructed.When the zoom motor 12 rotates, the zoom lens 1B moves and zoom isperformed.

As described above, according to the first to the third embodiments, thetransfer gate control unit (e.g. the timing generator 58 in FIG. 6)controls the potential φtx of the transfer gate so that a part of thecarriers overflowing from the photodiode PD flows into the floatingdiffusion region FD in the period from the timing T2 to T4 in which thephotodiode PD is generating and storing the carriers. At this time, thetransfer gate control unit may be formed on the same chip as that of thesolid image pickup device.

Moreover, in FIG. 4, the pixel signal generating unit of FIG. 4generates a pixel signal according to the carriers stored in thephotodiode PD and the carriers having overflowed from the photodiode PDinto the floating diffusion region FD.

Thereby, the ratio of the carriers flowing into the floating diffusionregion FD among the carriers overflowing from photodiode PD can becontrolled at high accuracy, and the dynamic range can be expanded aswell as the image quality can be improved. Moreover, both the structuresof the overflow from the photodiode PD into the floating diffusionregion FD, and of the overflow from the photodiode PD to the drain B arethe lateral overflow drain structures. Consequently, the difference ofthe temperature dependence of them can be reduced, and the ratio of thequantities of the carriers overflowing into the both can be easily keptto a fixed value by controlling the potential of the transfer gate.

Incidentally, any of the embodiments described is only an example of theconcretization at the time of implementing the present invention, andthe technical sphere of the present invention should not be interpretedto be limited by the embodiments. That is, the present invention can beimplemented in various modes without departing from the technical spritor the principal features thereof.

This application claims priority from Japanese Patent Application No.2005-008123 filed Jan. 14, 2005, which is hereby incorporated byreference herein.

1. An image pickup device, comprising: a photoelectric conversion unitgenerating carriers by photoelectric conversion and accumulating a partof said carriers; a transfer transistor for transferring carriers ofsaid photoelectric conversion unit; a floating diffusion region intowhich carriers of said photoelectric conversion unit transferred by saidtransfer transistor; a transfer gate control unit controlling a gatevoltage of said transfer transistor to be any of a first gate voltage atwhich said transfer transistor is turned on, a second gate voltage atwhich said transfer transistor is turned off, and a third gate voltagebetween the first and the second gate voltages; and a pixel signalgenerating unit generating a pixel signal based on the carrierstransferred into said floating diffusion region in a period in which thegate voltage is controlled to be the third gate voltage.
 2. An imagepickup device according to claim 1, wherein said transfer gate controlunit controls said third gate voltage of said transfer gate according toan amplification degree of the pixel signal corresponding to ISO speed.3. An image pickup device according to claim 1, wherein said transfergate control unit controls said third gate voltage of said transfer gateso that a height of a barrier under said transfer gate between saidphotoelectric conversion unit and said floating diffusion region is thelowest among heights of barriers enclosing said photoelectric conversionunit.
 4. An image pickup device according to claim 1, wherein Saiddevice further comprises a lateral overflow drain adjoining to saidphotoelectric conversion unit.
 5. An image pickup device according toclaim 4, wherein said transfer gate control unit controls said thirdgate voltage of said transfer gate so that a barrier under said transfergate may have a same height as that of an element isolation barrierbetween said photoelectric conversion unit and said lateral overflowdrain.
 6. An image pickup device according to claim 5, wherein saidheight of said barrier under said transfer gate and said elementisolation barrier between said photoelectric conversion unit and saidlateral overflow drain are lower than heights of barriers enclosing saidphotoelectric conversion unit.
 7. An image pickup device according toclaim 1, wherein said transfer gate control unit controls said thirdvoltage of said transfer gate according to a temperature.
 8. An imagepickup device, comprising: a photoelectric conversion unit generatingcarriers by photoelectric conversion and accumulating a part of saidcarriers; a transfer transistor for transferring carriers of saidphotoelectric conversion unit; a floating diffusion region into whichcarriers of said photoelectric conversion unit transferred by saidtransfer transistor; a transfer gate control unit controlling a gatevoltage of said transfer transistor so that carriers overflowing fromsaid photoelectric conversion unit for a period in which saidphotoelectric conversion unit is generating and accumulating carriersmay flow into said floating diffusion region; and a pixel signalgenerating unit generating a pixel signal based on carriers accumulatedin said photoelectric conversion unit and having overflowed into saidfloating diffusion region.
 9. A control method of an image pickup deviceprovided with a photoelectric conversion unit generating carriers byphotoelectric conversion and accumulating a part of said carriers, atransfer transistor for transferring carriers of the photoelectricconversion unit, and a floating diffusion region into which carriers ofsaid photoelectric conversion unit transferred by said transfertransistor, the method comprising: a transfer gate control step ofcontrolling a gate voltage of said transfer transistor so that carriersoverflowing from said photoelectric conversion unit for a period inwhich said photoelectric conversion unit is generating and accumulatingcarriers may flow into said floating diffusion region; and a pixelsignal generating step of generating a pixel signal based on carriersaccumulated in said photoelectric conversion unit and having overflowedinto said floating diffusion region.
 10. A camera, comprising: an imagepickup device according to claim 1; a lens for focusing an optical imageon said image pickup device; and a diaphragm for changing a lightquantity passing through said lens.